EP 1813783 B1, U.S. Pat. No. 8,677,961 B2, and U.S. Pat. No. 7,377,245 B2 disclose electric cam phasing systems.
FIG. 1a shows a cross-sectional side view of a conventional electric cam phasing system 100 and FIG. 1b shows an isometric view of a portion of system 100. Cam phasing system 100 includes an electric motor 102 for adjusting a position of a camshaft 106 relative to a sprocket 104. Sprocket 104 couples the camshaft 106 to a crankshaft via a chain, belt, or gearing. System 100 includes a drive element 108 at an end of a shaft 110 of motor 102 that is non-rotatably connected to an input shaft coupling 112 of a gearbox 114. Both ends of drive element 108 fit into a slot in the coupling 112 of the gearbox 114. During engine start-up and shutdown, rotation between camshaft 106, which includes a gearbox central bolt 116 therein, and gearbox input shaft coupling 112 could occur, changing the valve timing. Upon cold start conditions, the system 100 must learn its position, which takes a very short time but still requires movement of the camshaft to do so.